challenges of cost effective screening of current and future tmr/pmr design heads henry patland...
TRANSCRIPT
Challenges of cost effective screening of current and future TMR/PMR design heads
Henry Patland
President & CEO
www.us-isi.com
AbstractAs the industry makes the transition to PMR technology, with expected 100% transition by 2010, there are many challenges that head designers need to overcome to make this transition successful.
In addition to dealing with completely new head, media and channel designs, head manufacturers have to quickly anticipate the type of failures they will see from new head designs in volume production environments and be ready to cost effectively screen out those failures.
This presentation will concentrate on the challenges of testing these new head technologies, the type of solutions that are currently available and future requirements. Also a cost effective test strategy will be presented for discussion.
Outline GMR/LMR head technology overview TMR/PMR head technology overview Conventional quasi-static testing (QST) Specific problems for PMR/TMR heads Can QST testing address these specific problems for
TMR/PMR heads? Dynamic testing an alternative or complement to QST
testing Advantages/disadvantages of dynamic vs. QST testing Proposed cost efficient model for electrical head test Conclusion
GMR/LMR Heads
TMR/PMR
LMR vs. PMR Recording
LMR head sees zero field between transition and either a positive or negative field during transition
PMR head sees either positive or negative field between transitions and zero field during transition
LMR Transition Field Component
Structure of media stray field and read-back pulse for longitudinal recording
PMR Transition Field Component
Media stray fields for perpendicular media with soft under-layer
U-Shape bending caused by Perpendicular Stray Field
Low Frequency Cut-off in PMR
Read-back of low density perpendicular square wave pattern with different LF cut-off frequency: Signal shape distortions
Conventional QST Testing of both GMR/LMR and TMR/PMR Heads
High/Low resistance Low amplitude High asymmetry Barkh jump, hysteresis Low SNR Instability ESD damage (pin-layer-reversal)
QST Transfer Curve
Resistance
Amplitude
Asymmetry
Barkh Jump
Hysteresis
Bias Point
Delta R/R
Bias Angle
Slope
Max Slope
Parametrics extracted from QST Transfer Curve
Field Induced Instability
Soft Kink at 160 Oe
Field Induced Instability @ 150 Oe
Field Induced Instability @160 Oe
Field Induced Instability @ 170 Oe
Spectral Maximum Amplitude Noise (SMAN) Test
Patent: US6943545
Soft Kink at 160 Oe
Spectrum Analysis
Pin-Layer-Reversal due to ESD damage
QST has good track record at conventional testing.
Can QST testing address TMR/PMR Specific Problems?
PMR/TMR Specific Problems and Using QST Test Strategy
Pin-holes and µSmearing on insulating spacer Instability with lower cut off frequency Weak pin-layer Stray side field sensitivity and larger shield
geometries Writer pole problems
Problem: Pin-Hole & µSmearing Issues Both Pin-Holes and µSmearing occur during manufacturing of TMR
stacks with extremely thin insulation layer
Both Pin-Holes and µSmearing disrupt the tunneling mechanism and essentially create a short across the insulation layer
When Pin-Holes are present, some of the Bias current flows through the created shorts, and SNR is deteriorated
Additionally these shorts cause higher operating temperature of the TMR sensor which in turn causes reliability issues
Pin-Holes or µSmearing
QST Solution: Pin-Hole & µSmearing Issues By raising the TMR sensor temperature either
through Bias Source or external means, and measuring the Resistance change, both Pin-Hole & µSmearing can be detected
DeltaR/R, Transfer Curve, Hysteresis, and Slope of Transfer Curve are also good indicators of Pin-Hole or µSmearing presence
Problem: Lower Frequency Instability
Since PMR heads see more low frequency component and are exposed to multiple state magnetic fields between transitions, the probability of magnetic field induced instability is increased
This type of instability can cause high BER or losing servo in the drive
QST Solution: Lower Frequency instability
By lowering the cut-off freq to 100Khz from typical 3-5Mhz and using industry standard Spectral Maximum Amplitude Noise (SMAN) tests these unstable heads can be effectively screened out
Problem: Weakly Pinned Heads
If pinned layer is weak, the magnetization angle between pinned layer and free layer is compromised causing degraded DeltaR/R, SNR degradation and sensor instability
QST Solution: Weakly Pinned Heads
By testing heads at high magnetic fields and various angles, weakly pinned head can be screened out by QST
Weakly pinned heads might require additional re-initialization before final QST test
Problem: Stray Side Field sensitivity and New Larger Shield Geometries
Stray side field sensitivity can cause sensor saturation and transition shifts as caused by adjacent tracks
Larger shields absorb much of external magnetic field to shield the sensor and can also become magnetized causing sensor instability
QST Solution: Stray Side Field sensitivity and New Larger Shield Geometries
By testing QST with different magnetic field orientation, stray side field sensitivity can be simulated and sensitive heads can be screened out
By applying larger magnetic fields (typ: TMR/PMR – 500 to 600 Oe) the larger shields can be saturated to conventionally exercise the sensor
Problem: Writer Pole Design
Vertical Pole heads have poor write gradient
Write distortions when head is skewed with respect to track direction
Thin pole heads exhibit pole remnance problems due to magnetic domains in the pole tips (sometimes overwriting servo patterns)
QST Solutions: Writer Pole Design
With current technology QST is not capable of detecting this failure
Currently through improved writer pole material and geometry design, this issue is getting resolved
ISI Quasi-Static Testing Portfolio
Available Electrical Test Technologies
Dynamic Testing Quasi-Static Testing
Dynamic Head Test Advantages
Tests both writer and reader Resembles closely final head/media
arrangement Extensive tests such as MRR, Amp, Asym,
NLTS, SNR, OW, PW50, MRW, MWW, ATE, BER
Dynamic Head Test Disadvantages
High capital cost ($$$) Low UPH (typical 30-40) Media quality/flying height variation Difficult to separate writer vs. reader failures Can only be done at HGA level, high scrap cost High operating cost Larger and higher class cleanroom required Higher ESD danger due to more handling Poor correlation to final HDD yield
QST Head Test Advantages Low capital cost ($) High UPH (typical 1000) Can be done at row level (early test equals lower
scrap cost) Very detailed and effective reader testing with
and without various stresses Good correlation to final reader related HDD
Yield Low ESD risk due to automation Low operating cost Less clean room space and lower class
cleanroom required
QST Head Test Disadvantages
Cannot characterize writer Cannot predict head/media interface problems
since there is no flying No off-track analysis
Conventional Electrical Test Flow Model
100%
Bar/Slider
QST
100%
Dynamic Head Test
100%
Head Stack Actuator
QST
100%
Final HDD Test/Burn-in
Conventional Electrical Test Cost Model
Annual Slider
Volume(M) Yield
Test Type
ASP(K)
Number of Testers
Required
Annual Cost /w
5 Yr Depr.(M)
Slider UPH
%Of
Sliders Tested
Cost per slider
%Of Total
Test Cost3,947 70% QST Wafer $750 221 $33 3000 100% $0.017 5.56%3,036 80% QST Bar $150 729 $22 700 100% $0.011 3.66%2,530 85% DET HGA $250 10,630 $532 40 100% $0.266 89.06%2,200 90% QST HSA $45 1,138 $10 325 100% $0.005 1.72%2,000Total $0.30
Final HDD Yield
Re-work Cost
AvgHds/HDD
HDD Total(M)
Total Rework
Cost(M)
98.00% $3.00 2.50 800 $48
Note:Assumes 17hr/day tester utilizationAssumes Rework Cost labor only
Proposed Electrical Test Flow Model
100%
Bar/Slider
QST
5%
Dynamic Head Test
100%
Head Stack Actuator
QST
100%
Final HDD Test/Burn-in
Sampling or NO DET Testing
More Cost-Effective Test Cost Model
Annual Slider
Volume(M) Yield
Test Type
ASP(K)
Number of Testers
Required
Annual Cost /w 5 Yr
Depreciation(M)
Slider UPH
%Of
Sliders Tested
Cost per slider
%Of Total
Test Cost3,947 70% QST Wafer $750 221 $33 3000 100% $0.017 35.93%3,036 80% QST Bar $150 729 $22 700 100% $0.011 23.69%2,530 90% DET HGA $250 532 $27 40 5% $0.013 28.79%2,300 85% QST HSA $45 1,189 $11 325 100% $0.005 11.60%2,000Total $0.05
Final HDD Yield
Re-work Cost
AvgHds/HDD
HDD Total(M)
Total Rework
Cost(M)
95.00% $3.00 2.50 800 $120
Note:Assumes 17hr/day tester utilizationAssumes Rework Cost labor only
Conclusion Even though the final HDD yield is lowered in
the Proposed Test Model the total cost of annual DET cost and rework cost combined is: $147M vs. $580M in the Conventional Test Model
Quasi-Static Test is the cost effective test solutions for current and future TMR/PMR design heads
Can 100% DET testing be cost-effective?
References Alexander Taratorin, “Magnetic Recording Systems and
Measurements”, San Jose Research Center, HGST Bryan Oliver, Qing He, Xuefei Tang, and J. Nowaka), “Dielectric
breakdown in magnetic tunnel junctions having an ultrathin barrier”, JOURNAL OF APPLIED PHYSICS VOLUME 91, NUMBER 7
Sangmun Oh1, K. Nishioka2, H. Umezaki3, H. Tanaka1, T. Seki1, S. Sasaki1, T. Ohtsu2, K. Kataoka2, and K. Furusawa1 “The Behavior of Pinned Layers Using a High-Field Transfer Curve”, IEEE TRANSACTIONS ON MAGNETICS, VOL. 41, NO. 10, OCTOBER 2005
H. Patland, W. Ogle, “High Frequency Instabilities in GMR Heads Due to Metal-To-Metal Contact ESD Transients”, EOS/ESD Symposium 2002
Integral Solutions Int’l, “Quasi 97”, “Blazer-X5B” and “QST-2002” Tester